Blizzard just published a blog on the upcoming end of PvP Season 14--which could end in as little as two weeks. Past end-of-season announcements have been tied to new major patches, so it's reasonable to speculate that Season 14's end will be close to Patch 5.4.7's launch.

Season 15 will begin approximately a week after the end of Season 14.

As for Season 15 Prideful PvP gear, it's ilvl 550 and shares models with Season 14 PvP gear. However, the colors are swapped between factions so there's no faction-exclusive colors anymore.